The present invention relates to a printer capable of printing on a booklet such as a passbook having a plurality of sheets bound, and more particularly to a booklet printer suitable as a passbook printer which uses a non-impact printing system such as a thermal printing system.
In a printer for printing characters on a booklet such as passbook having a plurality of sheets bound, a wire dot printing system has been mainly used. For example, in Japanese Patent Examined Publication No. 59-15833, a passbook whose thickness differs depending on which page is being printed is pressed to a reference guide by a platen to keep a print plane at a constant position, and characters are printed by wire dot print means. This apparatus can make sharp print on a print medium having a variable thickness, but when the passbook is to be line-fed, the pressure to the passbook must be temporarily released. As a result, the operation time increases and it is an obstacle to improved printing performance.
Further, because of the wire dot printing system, the print noise is loud.
In order to resolve the print noise problem, it has been proposed to use a thermal print system. An example thereof is disclosed in Japanese Patent Unexamined Publication No. 56-34465. In this apparatus, a thermal print head is moved along a line to print characters on one line. When the passbook is to be line-fed after printing, it is necessary to release pressure to the thermal print head. As a result, it is difficult to improve printing performance as it is in the wire dot printing system.
A print system which does not need release of pressure to the thermal print head where the sheet is to be line-fed is shown in FIG. 1, in which a planar line dot type thermal print head 1 has heat generating resistors 2 corresponding to print elements, conductors 4, a driver 5 and a connector plannerly arranged on a substrate 3. As shown in FIG. 2, the thermal print head 1 is pressed by a spring 10 to a thermal carbon paper 7 on a platen roller 9. This apparatus has been known as a line dot type thermal printer.
In the print operation, the heat generating resistors of the thermal print head (thermal head) 1 are pressed to the thermal carbon paper 7 having thermally fusable ink applied thereon while a print sheet 8 is pressed to the platen roller 9 by the spring 10. The print sheet is fed by rotating the platen roller 9 to feed the print sheet 8 and the thermal carbon paper 7 together. Since it is not necessary to release the pressure to the thermal head when the print sheet is to be line-fed, a high speed print operation is attained.
However, when this print system is applied to a printer which prints characters near a seam area (folding line 12) of the passbook 11 having a plurality of sheets bound as shown in FIG. 3, the following problem arises.
The thickness of the passbook significantly changes around the folding line 12 and there is a large step at the folding line 12. In a passbook shown in FIG. 4, print lines 13a and 13b adjacent the folding line are usually spaced from the folding line by approximately 5 mm. The step between a first page 14 and an adjacent page 15 bordered by the folding line with the passbook 11 being in an open position may exceed 1.5 mm, although it differs depending on the particular page being printed on. Accordingly, when characters are to be printed by the known line dot type thermal printer as shown in FIG. 3 on print lines near the folding line 12 of the passbook the heat generating resistors 12 do not contact the thermal carbon paper 7 and the passbook 11 unless the passbook is pressed to the thermal head 1 with a very high pressure. Since the passbook usually has a thick sheet as a front sheet 16, the pressure required is necessarily high. If the platen roller 9 is rotated while the passbook and the thermal carbon paper are pressed with such high pressure, the print sheet 17 of the passbook (which is usually a relatively thin sheet) is staggered and warps as shown in FIG. 5. As for the thermal carbon paper 7, it usually has a film several microns thick as a base. If it is fed while the high pressure is applied thereto, creases are formed, and when the crease area comes to the print position, the film does not contact the passbook and characters are not printed. In order to resolve these problems, the pressure to the thermal head may be somewhat reduced, but since the contact between the thermal carbon paper and the thermal head is degraded, the characters printed are not sharp. In order to resolve this problem, an application time of pulses to the heat generating resistors of the thermal head may be lengthened to supply greater print energy. In this case, however, the print speed is reduced and the desired high speed printing is not attained.
In order to improve the contact between the passbook and the thermal head around the folding line of the passbook, it is necessary to press the thermal head to the passbook without significantly bending the passbook. As an approach thereto, an end surface type thermal head disclosed in Japanese Patent Unexamined Publication Nos. 60-24963 and 60-24965 and Japanese Utility Model Unexamined Publication No. 59-59342 may be used. A thickness of the end surface type thermal head is several mm. Thus, when characters are printed on the print lines around the folding line of the passbook, the thermal head does not abut against the step of the passbook.
However, the end surface type thermal head is more complex to manufacture and more expensive in manufacturing cost than the planar thermal head shown in FIG. 1. As a result, it is difficult to provide a low cost printer.